The invention relates to a method for the dynamic correction of an ignition point of an internal combustion engine having characteristic-diagram ignition as a function of intake tube pressure, intake air temperature and engine speed.
In internal combustion engines with electronic ignition, it is customary to record the ignition point in a characteristic diagram against the load and the engine speed In this way, an appropriate ignition point for the respective engine speed and for the load, e.g. an ignition point optimized for exhaust gas and consumption values, is taken from the characteristic diagram. Thus, for example, for idling an "early" ignition point is selected, which stabilizes idling by an increase in the torque, while for full-load operation an ignition point is selected which takes account of the knock border line.
Although such methods are suitable for the steady-state behavior of internal combustion engines, they have the disadvantage that the dynamic processes at the internal combustion engine, such as for example load and speed changes, are not adequately taken into account.
It is an object of the invention to correct ignition points determined from the characteristic diagram in such a way that optimized ignition points are available for the dynamic operation of the internal combustion engine.
The object is achieved according to the invention by providing a method wherein, if a predetermined intake tube pressure change (.DELTA.p) is exceeded, a correction ignition point (.DELTA..alpha..sub.retard) acting in the "retard" direction is superimposed within a selectable time (t.sub.2 -t.sub.1) on the instantaneously valid characteristic-diagram ignition point (.alpha..sub.2), and wherein the correction ignition point (.DELTA..alpha..sub.retard) is then adjusted within a freely selectable time in the "advance" direction to the valid characteristic-diagram ignition point (.alpha..sub.2).
In certain preferred embodiments the correction ignition point ).DELTA..alpha..sub.retard) is a function of intake air temperature (.theta..sub.air) In certain preferred embodiments the correction ignition point (.DELTA..alpha..sub.retard) is a function of the engine speed(n).
A sudden change in the operation of the internal combustion engine, i.e. a load change or a speed change, is detected via a jump in the intake tube pressure. Such a change can lead to knocking, in particular in the case of the changeover to full load and at high intake air temperatures. Although, in this case, the ignition point is matched to this operating state via the characteristic diagram, knocking can nevertheless occur due to the sudden load alteration under unfavorable conditions. In order to avoid knocking in all cases, a correction ignition point in the "retard" direction is superposed on the instantaneously valid characteristic-diagram ignition point. This correction value is selected so that knocking is reliably ruled out. The amount of the correction value is here a function of the intake air temperature and of the engine speed. Following this retardation of the ignition point, the correction value is reversed within a freely selectable time in the "advance" direction until the valid characteristic-diagram ignition point is reached.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.